Malignant meningioma with a new intracytoplasmic inclusion body.

A 55-year-old man presented with a frontal mass lesion, which histologically consisted of pleomorphic tumor cells with necrotic foci and abundant mitotic figures, showing a meningothelial pattern focally. In addition, many eosinophilic round- or irregular-shaped bodies were seen not only in tumor cell cytoplasm but also in between the tumor cells. By electron microscopy, the tumor cells showed a minimal adherence to each other and the intercellular spaces were wide. Tumor cells had numerous branching cytoplasmic processes and some of them were united by desmosomal junctions. These features suggested that the tumor was a malignant variety of arachnoid trabecular cell meningioma. The inclusion bodies consisted of homogeneous fine granular material and were not surrounded by microvilli. This type of inclusion body has not been reported in meningiomas in the past. The significance and possible pathogenesis of the inclusions are discussed.